This invention relates to electromagnetic interference shielding, and more particularly to a gasket for shielding such interference.
Electromagnetic interference (EMI) is a problem that is commonly encountered in the design and operation of electronic equipment. Standards have been set that limit the amount of allowable EMI emissions from electronic devices. To meet the emissions standards it is necessary to seal around doors, panels, and slots that hold expansion cards and connectors. This task is challenging in today""s commercial environment because there is pressure to minimize the spacing between slots and openings in order to increase the density of connection points to a particular piece of electronic equipment.
EMI containment problems have been exacerbated as processing speeds of electronic equipment have increased because EMI can cause electronic equipment to malfunction or not function at all. For example, contemporary electronic communications equipment operate at very high frequencies and equipment packaging attempts to concentrate a relatively large amount of circuitry per frame of equipment. Each frame tends to act as a transmitting source of EMI to the environment and more so as frequencies become higher (i.e., wavelengths become smaller).
In the majority of cases, the solution to the problem consists of enclosing the frames of equipment in a properly grounded metal box. These metal boxes usually comprise a metal frame on which metal panels may be removably secured to allow access to the equipment on the frame. In order to provide adequate EMI shielding, the mating surfaces of these panels must be electrically connected together. This is usually achieved through the use of an EMI gasket which provides an interface between mating conductive surfaces. The gasket should provide high conductivity to ensure DC continuity between mating surfaces and is usually compressible.
One known gasket is made from conductive rubber, which is inserted into a channel between two mating surfaces. Alternatively, the gasket may be glued to the inside of the channel. In such an arrangement, the channel is used to give the gasket lateral stability and to prevent its misalignment which could result through repeated removal and replacement of the panels. Another method of shielding box panels is through the use of a metallized compressible gasket attached to a metal band along its length. The metal band is secured to one of the mating surfaces so that the gasket is sandwiched between the mating surfaces when a panel is attached to the frame.
Another example of an EMI shield is illustrated in U.S. Pat. No. 5,161,997, to Defibaugh et al. The Defibaugh et al. EMI shield has opposed edges formed into a pair connector receiving of channels. The lower channel of the shield receives a connector, which is secured to the shield by rotating the connector toward the shield such that a rear face of the shield contacts front face of the connector. Next, an extending upper tab of the shield is bent over an upper edge of the connector, forming an upper channel, to secure the connector to the shield. While the Defibaugh et al. is disclosed as being a xe2x80x9chardwarelessxe2x80x9d connector (i.e., it may be mounted without additional hardware), it requires secondary tooling to form the upper channel after connector insertion.
These methods of EMI control are fully operable for their intended purpose. However, there still remains a need for an improved EMI shield that allows for higher densities of connection points to electronic equipment, and that is capable of providing an adequate level of protection against emissions. Further, there is a need for a shielding gasket that provides for easy mounting to connectors without requiring additional tooling or hardware. The present invention provides such a solution.
The present invention is directed to a gasket for reducing electromagnetic emission from electronic equipment. The gasket is defined by a substantially rectangular body that includes one or more openings through which a portion of a connector, to which the gasket is mounted, may pass. The gasket includes a hook-shaped peripheral edge, a plurality of projections, a plurality of retaining clips, and tabs that are formed on opposing sides the opening(s). The hook-shaped edge, projections and retaining clips are adapted to receive and secure a connector to the gasket, and the tabs are provide to make an electrical contact with the connector housing. The clips and projections may engage the holes provided in the connector flange to enhance the integrity of the system. Additionally, the gasket includes spring fingers for use in mounting the gasket to a bulkhead and for forming an electrical contact with the bulkhead. The spring fingers provide for additional points of contact.
The above-noted structure of the gasket of the present invention further provides for easy attachment of connectors to the gasket without the use of additional mounting hardware.
Other features and aspects will be described herein.